U.S. patent application number 12/681500 was filed with the patent office on 2010-09-23 for electrolytic manganese dioxide for lithium primary battery, manufacturing method therefor, and lithium primary battery using same.
Invention is credited to Toshiyuki Shimizu, Yasuhiro Suzuki, Shinichiro Tahara.
Application Number | 20100239911 12/681500 |
Document ID | / |
Family ID | 41506846 |
Filed Date | 2010-09-23 |
United States Patent
Application |
20100239911 |
Kind Code |
A1 |
Tahara; Shinichiro ; et
al. |
September 23, 2010 |
ELECTROLYTIC MANGANESE DIOXIDE FOR LITHIUM PRIMARY BATTERY,
MANUFACTURING METHOD THEREFOR, AND LITHIUM PRIMARY BATTERY USING
SAME
Abstract
Electrolytic manganese dioxide for lithium primary batteries has
a sodium content of 0.05 to 0.2% by mass, and a pH of 5 to 7 as
measured according to JIS-K-1467. Using this electrolytic manganese
dioxide as a positive electrode active material for lithium primary
batteries enables the batteries to be excellent in both initial
discharge characteristics and long-term discharge
characteristics.
Inventors: |
Tahara; Shinichiro; (Osaka,
JP) ; Suzuki; Yasuhiro; (Kyoto, JP) ; Shimizu;
Toshiyuki; (Osaka, JP) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, NW
WASHINGTON
DC
20005-3096
US
|
Family ID: |
41506846 |
Appl. No.: |
12/681500 |
Filed: |
July 6, 2009 |
PCT Filed: |
July 6, 2009 |
PCT NO: |
PCT/JP2009/003122 |
371 Date: |
April 2, 2010 |
Current U.S.
Class: |
429/224 ;
205/539 |
Current CPC
Class: |
H01M 4/505 20130101;
C01G 45/02 20130101; Y02E 60/10 20130101; H01M 4/382 20130101; H01M
6/16 20130101; H01M 4/1391 20130101; H01M 4/131 20130101; C01P
2006/40 20130101; H01M 6/14 20130101; H01M 2004/028 20130101; Y10T
29/49108 20150115; Y02P 70/50 20151101; H01M 4/502 20130101 |
Class at
Publication: |
429/224 ;
205/539 |
International
Class: |
H01M 4/50 20100101
H01M004/50; C25B 1/21 20060101 C25B001/21 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 9, 2008 |
JP |
2008-178819 |
Claims
1. Electrolytic manganese dioxide for lithium primary batteries,
the electrolytic manganese dioxide having a sodium content of 0.05
to 0.2% by mass, and a pH of 5 to 7 as measured according to
JIS-K-1467.
2. A method for producing electrolytic manganese dioxide for
lithium primary batteries, the method comprising: preparing
neutralized electrolytic manganese dioxide by neutralizing
electrolytic manganese dioxide with sodium hydroxide, the
electrolytic manganese dioxide being electrosynthesized in an acid
electrolytic bath; and washing the neutralized electrolytic
manganese dioxide with water in such a manner that water-washed
electrolytic manganese dioxide has a sodium content of 0.05 to 0.2%
by mass, and a pH of 5 to 7 as measured according to
JIS-K-1467.
3. The method of claim 2, wherein the neutralized electrolytic
manganese dioxide has a sodium content of 0.1 to 0.4% by mass.
4. A lithium primary battery comprising: a positive electrode using
the electrolytic manganese dioxide for lithium primary batteries of
claim 1; a negative electrode using one of lithium metal and a
lithium alloy; and a separator and a non-aqueous electrolytic
solution between the positive electrode and the negative electrode.
Description
RELATED APPLICATIONS
[0001] This application is the U.S. National Phase under 35 U.S.C.
.sctn.371 of International Application No. PCT/JP2009/003122, filed
on Jul. 6, 2009, which in turn claims the benefit of Japanese
Application No. 2008-178819, filed on Jul. 9, 2008, the disclosures
of which Applications are incorporated by reference herein.
TECHNICAL FIELD
[0002] The present invention relates to electrolytic manganese
dioxide for lithium primary batteries, manufacturing method
therefor, and a lithium primary battery using the same as a
positive electrode active material.
BACKGROUND ART
[0003] Lithium primary batteries use lithium and other light metals
as a negative electrode active material, and manganese dioxide or
graphite fluoride as a positive electrode active material. These
batteries have unique features including high voltage, high energy
density, low self-discharge, and an extremely long storage life,
and hence are used in various electronic devices.
[0004] Among the materials used as a positive electrode active
material, manganese dioxide is very popular because it is
inexpensive and abundant, and as a positive electrode active
material for lithium primary batteries, electrolytic manganese
dioxide is commonly used due to its excellent discharge performance
and long-term storage performance.
[0005] Electrolytic manganese dioxide is generally electrolytically
synthesized in a sulphuric acid solution containing manganese ions,
and therefore, is required to be neutralized with alkali when used
as a positive electrode active material for lithium primary
batteries. Popular examples of the alkali used for neutralization
are ammonia and sodium hydroxide.
[0006] Electrolytic manganese dioxide prepared by neutralization
with ammonia (hereinafter, ammonia-neutralized product) is widely
used for lithium primary batteries. The ammonia-neutralized
product, however, is manufactured by only a few manufacturers, and
therefore, is less available and more expensive than electrolytic
manganese dioxide prepared by neutralization with sodium hydroxide
(hereinafter, sodium-neutralized product). As another disadvantage,
when used as a positive electrode active material for lithium
primary batteries, the ammonia-neutralized product requires a
dedicated exhaust system to ensure working conditions because it
causes ammonia to volatize, giving off a pungent smell when
heat-treated to remove moisture.
[0007] The sodium-neutralized product, on the other hand, is mainly
used as a positive electrode active material for dry batteries. The
sodium-neutralized product generally contains 0.3 to 0.5% by mass
of sodium, which may reduce the discharge performance when used for
lithium primary batteries. The reason for the reduction is that the
sodium in the sodium-neutralized product is deposited on the
lithium used as a negative electrode active material and forms a
resistance film thereon. The deposition is more significant as the
battery is stored at a higher temperature and for a longer period.
This is why the sodium-neutralized product is little used as a
positive electrode active material for lithium primary batteries
although it is easily available.
[0008] The sodium-neutralized product, however, is inexpensive and
mass-produced, and therefore, it is a valuable attempt from an
industrial viewpoint to make full use of this product as
electrolytic manganese dioxide for lithium primary batteries.
[0009] To achieve this attempt, it has been suggested that
electrolytic manganese dioxide is sodium-neutralized in such a
manner that the neutralized electrolytic manganese dioxide has a
minimum sodium content in the range of 0.05 to 0.2% by mass (Patent
Literature 1, for example).
[0010] The sodium-neutralized product having a minimum sodium
content, however, contains a large amount of sulfuric acid
residues, making its pH as low as 2 to 4. When sintered and used as
a positive electrode active material for lithium primary batteries,
such a sodium-neutralized product with a low pH increases the
battery internal resistance when a weak discharge is continued for
a long time such as over one year, although its initial discharge
performance is excellent.
[0011] Patent Literature 1: Japanese Patent Unexamined Publication
No. 2001-236957
SUMMARY OF THE INVENTION
[0012] The present invention relates to electrolytic manganese
dioxide for lithium primary batteries prepared from a
sodium-neutralized product. The invention has an object of
providing electrolytic manganese dioxide that offers both excellent
initial discharge characteristics and excellent long-term discharge
performance when used for a lithium primary battery, a method for
producing the electrolytic manganese dioxide, and a lithium primary
battery using the electrolytic manganese dioxide as a positive
electrode active material, thereby being excellent in long-term
discharge performance.
[0013] The electrolytic manganese dioxide for lithium primary
batteries according to the present invention has a sodium content
of 0.05 to 0.2% by mass, and a pH of 5 to 7 as measured according
to JIS-K-1467. The lithium primary battery using the electrolytic
manganese dioxide according to the present invention as a positive
electrode active material can reduce an increase in the battery
internal resistance even when a weak discharge is continued for a
long time such as over one year.
[0014] The method for producing the electrolytic manganese dioxide
for lithium primary batteries according to the present invention
includes preparing neutralized electrolytic manganese dioxide by
neutralizing electrolytic manganese dioxide with sodium hydroxide,
the electrolytic manganese dioxide being electrosynthesized in an
acid electrolytic bath; and washing the neutralized electrolytic
manganese dioxide with water in such a manner that water-washed
electrolytic manganese dioxide has a sodium content of 0.05 to 0.2%
by mass, and a pH of 5 to 7 as measured according to
JIS-K-1467.
[0015] The lithium primary battery according to the present
invention uses, as a positive electrode active material,
electrolytic manganese dioxide having a sodium content of 0.05 to
0.2% by mass, and a pH of 5 to 7 as measured according to
JIS-K-1467. Using this electrolytic manganese dioxide can reduce
the formation of a resistance film containing sodium or manganese
on the negative electrode, enabling the lithium primary battery to
be excellent in both initial discharge performance and long-term
discharge performance.
BRIEF DESCRIPTION OF THE DRAWING
[0016] FIG. 1 is a schematic sectional view of a lithium primary
battery according to an embodiment of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
[0017] The following is a description of an embodiment of the
present invention. Note that the following embodiment is one
example of the present invention, and does not limit the technical
scope of the invention.
[0018] The sodium content of the electrolytic manganese dioxide for
lithium primary batteries is measured by ICP analysis. In the case
of producing a lithium primary battery using the electrolytic
manganese dioxide prepared from a sodium-neutralized product as a
positive electrode active material, sodium elutes from the
electrolytic manganese dioxide when its sodium content is larger
than 0.2% by mass. The eluted sodium is deposited on the lithium
used as the negative electrode active material and forms a
resistance film thereon, reducing the battery discharge
performance. When the electrolytic manganese dioxide has a pH of
less than 5 as measured according to JIS-K-1467, sulfuric acid
components remaining in the electrolytic manganese dioxide react
with the small amount of water in the battery and generate an acid,
causing manganese ions to elute from the electrolytic manganese
dioxide during a long discharge. The eluted manganese ions are
deposited on the lithium used as the negative electrode active
material and form resistance film thereon, causing an increase in
battery internal resistance.
[0019] Note that it is impossible to produce electrolytic manganese
dioxide having a pH greater than 7 and a sodium content of 0.05 to
0.2% by mass by means of electrolyzing it in an acid electrolytic
bath and then sodium-neutralizing it.
[0020] Also note that when the sodium content of the
sodium-neutralized product is less than 0.05% by mass, it is
difficult to have a pH of 5 or greater by an after-mentioned
washing treatment with water.
[0021] The following is a brief description of the pH measurement
method specified in JIS-K-1467. First, 15 g of manganese dioxide as
a sample is put in a 200 ml Erlenmeyer flask, and 75 ml of a 20%
aqueous NH.sub.4Cl solution is added thereto so as to prepare a
sample solution. The aqueous NH.sub.4Cl solution contains 100 ml of
water and 20 g of NH.sub.4Cl dissolved therein. Next, the sample
solution is stirred with a magnetic stirrer for 30 minutes. The
stirring is performed at a rate that does not cause the solution to
spatter in the flask. After the stirring, the flask is left for
five to ten minutes at an inclination angle of 30 degrees. Then, 50
ml of the supernatant solution is collected and measured for its pH
by a digital pH meter or the like. The obtained value is considered
to be the pH of the manganese dioxide.
[0022] The following is a description of a method for measuring a
sodium content by ICP analysis. First, 1 g of manganese dioxide as
a sample is put in a 200 ml beaker, and 20 ml of hydrochloric acid
(a 50% by volume aqueous solution) is added thereto. The resulting
solution is heated until the manganese dioxide is dissolved, and
then cooled. The cooled solution is filtered, and pure water is
added thereto so as to make 100 ml of the solution. The resulting
solution is subjected to standard addition method using an atomic
absorption spectrometer so as to determine the quantity of
sodium.
[0023] The following is a description of a method for producing the
electrolytic manganese dioxide for lithium primary batteries
according to the embodiment.
[0024] First, electrolytic manganese dioxide is prepared which is
electrosynthesized in an acid electrolytic bath containing a
sulphuric acid solution. Then, the electrolytic manganese dioxide
is neutralized with aqueous sodium hydroxide so as to prepare
neutralized electrolytic manganese dioxide. The neutralization is
performed using aqueous sodium hydroxide that contains 2.0 to 10.0
g of sodium hydroxide per 1 kg of electrolytic manganese dioxide.
As a result, the neutralized electrolytic manganese dioxide has a
sodium content of 0.05 to 0.5% by mass. The neutralized
electrolytic manganese dioxide thus obtained generally has a pH of
2 to 4 as measured according to JIS-K-1467.
[0025] Next, the neutralized electrolytic manganese dioxide is
stirred and washed with water, centrifuged to remove water, and
dried, thus preparing water-washed electrolytic manganese dioxide.
The washing is performed in such a manner that the water-washed
electrolytic manganese dioxide has a sodium content of 0.05 to 0.2%
by mass, and a pH of 5 to 7 as measured according to
JIS-K-1467.
[0026] When a large amount of sodium hydroxide is used for the
neutralization, and as a result, the sodium content of the
neutralized electrolytic manganese dioxide is 0.4 to 0.5% by mass,
a large amount of water is required for washing to make the sodium
content of the water-washed electrolytic manganese dioxide 0.2% by
mass or less. In the contrary, when a small amount of sodium
hydroxide is used for the neutralization, and as a result, the
sodium content of the neutralized electrolytic manganese dioxide is
0.05% by mass or more and less than 0.1% by mass, the neutralized
electrolytic manganese dioxide has a low pH. In this case, a large
amount of water is required to wash out sulfuric acid components
and to make the water-washed electrolytic manganese dioxide have a
pH of 5 or greater. Therefore, to save water for the washing, the
sodium content of the neutralized electrolytic manganese dioxide is
preferably 0.1 to 0.4% by mass.
[0027] In general, when manganese dioxide is used as a positive
electrode active material for lithium primary batteries, it is
necessary to remove the water in the crystal of the manganese
dioxide by a heat treatment at 300.degree. C. or above. In the
method for producing electrolytic manganese dioxide for lithium
primary batteries according to the present invention, the heat
treatment can be performed either before or after washing because
it does not change the sodium content or the pH of the electrolytic
manganese dioxide or affect the battery characteristics.
[0028] A lithium primary battery shown in FIG. 1 is produced using
as a positive electrode active material the electrolytic manganese
dioxide prepared as described above. FIG. 1 is a schematic
sectional view of the lithium primary battery according to the
embodiment of the present invention.
[0029] This lithium primary battery includes positive electrode 1
containing the above-described electrolytic manganese dioxide as an
active material, and negative electrode 2 containing lithium as an
active material. Positive electrode 1 and negative electrode 2 are
spirally wound together with separator 3 therebetween so as to form
an electrode assembly. The electrode assembly is put into case 9
together with a non-aqueous electrolytic solution (not shown). Case
9 has an opening sealed with sealing plate 8, which is joined to
lead 4 connected to the core sheet of positive electrode 1. Case 9
is also joined to lead 5 connected to negative electrode 2. The
electrode assembly is provided with upper insulating plate 6 and
lower insulating plate 7 for internal short circuit protection.
[0030] Positive electrode 1 is produced as follows. The
electrolytic manganese dioxide prepared by neutralization and
washing with water as described above is mixed with a conductive
agent, added with a binder and water, and then kneaded together to
prepare a positive-electrode mixture. The conductive agent can be
graphite powder such as artificial graphite or natural graphite, or
a mixture of graphite powder and carbon black such as acetylene
black. The amount of the conductive agent to be used can be large
enough to fully inject the electrolytic manganese dioxide and to
form a conductive path so as to reduce the electric resistance of
positive electrode 1. In particular, it is preferable that the
conductive agent contains 4 to 8 parts by weight of graphite per
100 parts by weight of the electrolytic manganese dioxide. Next,
the positive-electrode mixture is injected into a core sheet having
a mesh structure or fine pores such as an expanded metal, a net, or
a perforated metal, then rolled, and cut in size. Then, part of the
positive-electrode mixture is peeled off to which lead 4 is welded,
thereby producing belt-shaped positive electrode 1.
[0031] Negative electrode 2, on the other hand, which is also
belt-shaped, is composed of metallic lithium or a lithium alloy
such as Li--Al, Li--Sn, Li--NiSi, or Li--Pb.
[0032] The solvent of the non-aqueous electrolytic solution is not
particularly limited as long as it is an organic solvent generally
used in a non-aqueous electrolytic solution for lithium batteries.
More specifically, it is possible to use .gamma.-butyrolactone,
propylene carbonate, ethylene carbonate, or 1,2-dimethoxyethane
either alone or in combination.
[0033] The non-aqueous electrolytic solution contains a supporting
electrolyte, which can be lithium tetrafluoroborate, lithium
phosphorus hexafluoride, lithium trifluoromethanesulfonate, or
LiN(CF.sub.3SO.sub.2).sub.2, LiN(C.sub.2F.sub.5SO.sub.2).sub.2, or
LiN(CF.sub.3SO.sub.2)(C.sub.4F.sub.9SO.sub.2) having an imide bond
in the molecular structure.
[0034] Separator 3 can be made of a woven or nonwoven polyolefin
cloth, a microporous film, or the like.
[0035] The effect of the embodiment will be described in specific
examples below. The electrolytic manganese dioxide, which has been
prepared by electrolyzation in a sulfuric acid bath is neutralized
by adjusting the concentration in the aqueous sodium hydroxide to
contain 3.0 g of sodium hydroxide per 1 kg of the electrolytic
manganese dioxide. The neutralized electrolytic manganese dioxide
has a sodium content of 0.10% by mass. The neutralized electrolytic
manganese dioxide is filtered, dried, and heat-treated at
400.degree. C. for four hours. Then, the heat-treated electrolytic
manganese dioxide is stirred and washed with water which is added
in a ratio of 10 kg per 1 kg of the heat-treated electrolytic
manganese dioxide. After the washing with water, the electrolytic
manganese dioxide is centrifuged to remove water, and dried, thus
preparing water-washed electrolytic manganese dioxide having a
sodium content of 0.05% by mass, and a pH of 5.0 as measured
according to JIS-K-1467.
[0036] To be used as a positive electrode active material, the
water-washed electrolytic manganese dioxide is added with 5% by
mass of graphite as a conductive agent, and 2% by mass of
polytetrafluoroethylene as a binder. Then, the resulting mixture is
kneaded together with 35% by mass of pure water so as to prepare a
wet positive-electrode mixture. The wet positive-electrode mixture
and a 0.1 mm thick stainless expanded metal are fed together
between two rotating rollers rotating at the same speed so as to
inject the positive-electrode mixture into the expanded metal,
thereby producing a mixture sheet. The mixture sheet is dried,
rolled by a roller press, and cut in size (0.40 mm in thickness, 26
mm in width, and 235 mm in length), thereby preparing positive
electrode 1.
[0037] Negative electrode 2 is a lithium metal plate, which is cut
in size (0.18 mm in thickness, 24 mm in width, and 260 mm in
length). Positive electrode 1 and negative electrode 2 thus
prepared are spirally wound together with the separator made of a
microporous polyethylene film, thus forming the electrode assembly.
The electrode assembly is put into case 9. Next, stainless lead 4
connected to the core sheet of positive electrode 1 is connected to
the positive terminal of sealing plate 8, and nickel lead 5
connected to negative electrode 2 is connected to case 9. Then, the
unillustrated non-aqueous electrolytic solution is injected into
case 9, and the opening of case 9 is sealed. As a result, a
cylindrical manganese dioxide lithium primary battery shown in FIG.
1 is obtained which has a diameter of 17 mm and a height of 33.5
mm. Ten such batteries are produced. The non-aqueous electrolytic
solution is prepared by dissolving lithium
trifluoromethanesulfonate as a supporting electrolyte at a
concentration of 0.5 mol/L in a non-aqueous solvent. The
non-aqueous solvent is a mixed solvent of propylene carbonate and
dimethoxyethane in a volume ratio of 1:1. The manganese dioxide
lithium primary batteries thus produced are referred to as
batteries "A".
[0038] The electrolytic manganese dioxide, which has been prepared
by electrolyzation in a sulfuric acid bath is neutralized by
adjusting the concentration in the aqueous sodium hydroxide to
contain 7.0 g of sodium hydroxide per 1 kg of the electrolytic
manganese dioxide. The neutralized electrolytic manganese dioxide
has a sodium content of 0.30% by mass. The neutralized electrolytic
manganese dioxide is filtered, dried, and heat-treated at
400.degree. C. for four hours. Then, the heat-treated electrolytic
manganese dioxide is stirred and washed with water which is added
in a ratio of 10 kg per 1 kg of the heat-treated electrolytic
manganese dioxide. After the washing with water, the electrolytic
manganese dioxide is centrifuged to remove water, and dried, thus
preparing water-washed electrolytic manganese dioxide having a
sodium content of 0.20% by mass, and a pH of 5.0 as measured
according to JIS-K-1467. Batteries "B" are produced using the
water-washed electrolytic manganese dioxide thus obtained, but
otherwise in the same manner as batteries "A".
[0039] The electrolytic manganese dioxide, which has been prepared
by electrolyzation in a sulfuric acid bath is neutralized by
adjusting the concentration in the aqueous sodium hydroxide to
contain 9.0 g of sodium hydroxide per 1 kg of the electrolytic
manganese dioxide. The neutralized electrolytic manganese dioxide
has a sodium content of 0.40% by mass. The neutralized electrolytic
manganese dioxide is filtered, dried, and heat-treated at
400.degree. C. for four hours. Then, the heat-treated electrolytic
manganese dioxide is stirred and washed with water which is added
in a ratio of 20 kg per 1 kg of the heat-treated electrolytic
manganese dioxide. After the washing with water, the electrolytic
manganese dioxide is centrifuged to remove water, and dried, thus
preparing water-washed electrolytic manganese dioxide having a
sodium content of 0.20% by mass, and a pH of 7.0 as measured
according to JIS-K-1467. Batteries "C" are produced using the
water-washed electrolytic manganese dioxide thus obtained, but
otherwise in the same manner as batteries "A".
[0040] The electrolytic manganese dioxide, which has been prepared
by electrolyzation in a sulfuric acid bath is neutralized by
adjusting the concentration in the aqueous sodium hydroxide to
contain 4.0 g of sodium hydroxide per 1 kg of the electrolytic
manganese dioxide. The neutralized electrolytic manganese dioxide
has a sodium content of 0.15% by mass. The neutralized electrolytic
manganese dioxide is filtered, dried, and heat-treated at
400.degree. C. for four hours. Then, the heat-treated electrolytic
manganese dioxide is stirred and washed with water which is added
in a ratio of 20 kg per 1 kg of the heat-treated electrolytic
manganese dioxide. After the washing with water, the electrolytic
manganese dioxide is centrifuged to remove water, and dried, thus
preparing water-washed electrolytic manganese dioxide having a
sodium content of 0.05% by mass, and a pH of 7.0 as measured
according to JIS-K-1467. Batteries "D" are produced using the
water-washed electrolytic manganese dioxide thus obtained, but
otherwise in the same manner as batteries "A".
[0041] The electrolytic manganese dioxide, which has been prepared
by electrolyzation in a sulfuric acid bath is neutralized by
adjusting the concentration in the aqueous sodium hydroxide to
contain 5.0 g of sodium hydroxide per 1 kg of the electrolytic
manganese dioxide. The neutralized electrolytic manganese dioxide
has a sodium content of 0.20% by mass. The neutralized electrolytic
manganese dioxide is filtered, dried, and heat-treated at
400.degree. C. for four hours. Then, the heat-treated electrolytic
manganese dioxide is stirred and washed with water which is added
in a ratio of 10 kg per 1 kg of the heat-treated electrolytic
manganese dioxide. After the washing with water, the electrolytic
manganese dioxide is centrifuged to remove water, and dried, thus
preparing water-washed electrolytic manganese dioxide having a
sodium content of 0.10% by mass, and a pH of 6.0 as measured
according to JIS-K-1467. Batteries "E" are produced using the
water-washed electrolytic manganese dioxide thus obtained, but
otherwise in the same manner as batteries "A".
[0042] The electrolytic manganese dioxide, which has been prepared
by electrolyzation in a sulfuric acid bath is neutralized by
adjusting the concentration in the aqueous sodium hydroxide to
contain 9.0 g of sodium hydroxide per 1 kg of the electrolytic
manganese dioxide. The neutralized electrolytic manganese dioxide
has a sodium content of 0.40% by mass. The neutralized electrolytic
manganese dioxide is filtered, dried, and heat-treated at
400.degree. C. for four hours. Then the heat-treated electrolytic
manganese dioxide is stirred and washed with water which is added
in a ratio of 10 kg per 1 kg of the heat-treated electrolytic
manganese dioxide. After the washing with water, the electrolytic
manganese dioxide is centrifuged to remove water, and dried, thus
preparing water-washed electrolytic manganese dioxide having a
sodium content of 0.25% by mass, and a pH of 6.0 as measured
according to JIS-K-1467. Batteries "F" are produced using the
water-washed electrolytic manganese dioxide thus obtained, but
otherwise in the same manner as batteries "A".
[0043] The electrolytic manganese dioxide, which has been prepared
by electrolyzation in a sulfuric acid bath is neutralized by
adjusting the concentration in the aqueous sodium hydroxide to
contain 5.0 g of sodium hydroxide per 1 kg of the electrolytic
manganese dioxide. The neutralized electrolytic manganese dioxide
has a sodium content of 0.15% by mass. The neutralized electrolytic
manganese dioxide is filtered, dried, and heat-treated at
400.degree. C. for four hours. Then, the heat-treated electrolytic
manganese dioxide is stirred and washed with water which is added
in a ratio of 5 kg per 1 kg of the heat-treated electrolytic
manganese dioxide. After the washing with water, the electrolytic
manganese dioxide is centrifuged to remove water, and dried, thus
preparing water-washed electrolytic manganese dioxide having a
sodium content of 0.10% by mass, and a pH of 4.5 as measured
according to JIS-K-1467. Batteries "G" are produced using the
water-washed electrolytic manganese dioxide thus obtained, but
otherwise in the same manner as batteries "A".
[0044] The electrolytic manganese dioxide, which has been prepared
by electrolyzation in a sulfuric acid bath is neutralized by
adjusting the concentration in the aqueous sodium hydroxide to
contain 5.0 g of sodium hydroxide per 1 kg of the electrolytic
manganese dioxide. The neutralized electrolytic manganese dioxide
has a sodium content of 0.20% by mass. The neutralized electrolytic
manganese dioxide is filtered, dried, and heat-treated at
400.degree. C. for four hours. The heat-treated electrolytic
manganese dioxide has a pH of 4.5 as measured according to
JIS-K-1467. Batteries "H" are produced using the heat-treated
electrolytic manganese dioxide without being washed with water, but
otherwise in the same manner as batteries "A".
[0045] The electrolytic manganese dioxide, which has been prepared
by electrolyzation in a sulfuric acid bath is neutralized by
adjusting the concentration in the aqueous sodium hydroxide to
contain 1.5 g of sodium hydroxide per 1 kg of the electrolytic
manganese dioxide. The neutralized electrolytic manganese dioxide
has a sodium content of 0.05% by mass. The neutralized electrolytic
manganese dioxide is filtered, dried, and heat-treated at
400.degree. C. for four hours. Then, the heat-treated electrolytic
manganese dioxide is stirred and washed with water which is added
in a ratio of 20 kg per 1 kg of the heat-treated electrolytic
manganese dioxide. After the washing with water, the electrolytic
manganese dioxide is centrifuged to remove water, and dried, thus
preparing water-washed electrolytic manganese dioxide having a
sodium content of 0.03% by mass, and a pH of 4.5 as measured
according to JIS-K-1467. Batteries "I" are produced using the
water-washed electrolytic manganese dioxide thus obtained, but
otherwise in the same manner as batteries "A".
[0046] The electrolytic manganese dioxide that has not been
neutralized with aqueous sodium hydroxide has a sodium content of
0.01% by mass. This electrolytic manganese dioxide is heat-treated
at 400.degree. C. for four hours. The heat-treated electrolytic
manganese dioxide is stirred and washed with water which is added
in a ratio of 10 kg per 1 kg of the heat-treated electrolytic
manganese dioxide. After the washing with water, the electrolytic
manganese dioxide is centrifuged to remove water, and dried, thus
preparing water-washed electrolytic manganese dioxide. This
water-washed electrolytic manganese dioxide has a sodium content of
0.01% by mass, which is the same as before being washed with water,
and has a pH of 2.0 as measured according to JIS-K-1467. Batteries
"J" are produced using the water-washed electrolytic manganese
dioxide thus obtained, but otherwise in the same manner as
batteries "A".
[0047] The electrolytic manganese dioxide, which has been prepared
by electrolyzation in a sulfuric acid bath is neutralized by
adjusting the concentration in the aqueous sodium hydroxide to
contain 10.0 g of sodium hydroxide per 1 kg of the electrolytic
manganese dioxide. The neutralized electrolytic manganese dioxide
has a sodium content of 0.50% by mass. The neutralized electrolytic
manganese dioxide is filtered, dried, and heat-treated at
400.degree. C. for four hours. Then the heat-treated electrolytic
manganese dioxide is stirred and washed with water which is added
in a ratio of 40 kg per 1 kg of the heat-treated electrolytic
manganese dioxide. After the washing with water, the electrolytic
manganese dioxide is centrifuged to remove water, and dried, thus
preparing water-washed electrolytic manganese dioxide having a
sodium content of 0.20% by mass, and a pH of 7.0 as measured
according to JIS-K-1467. Batteries "K" are produced using the
water-washed electrolytic manganese dioxide thus obtained, but
otherwise in the same manner as batteries "A".
[0048] Five of each of the batteries "A" to "K" thus produced are
subjected to discharge at 500 mA at room temperature. The other
five of each of the batteries "A" to "K" are subjected to
constant-resistance discharge at 300 kg.OMEGA. at room temperature
and measured for internal resistance one year later. Table 1 below
shows the sodium contents of the electrolytic manganese dioxides
before and after being washed with water, the pH of the
electrolytic manganese dioxides after being washed with water. Note
that each value indicates a mean value of five batteries.
TABLE-US-00001 TABLE 1 internal resistance one year later sodium
content discharge when (% by mass) at discharged before after 500
mA.sup.(note 1) at 300 k.OMEGA..sup.(note 2) washing washing pH
(initial) (.OMEGA.) batteries A 0.10 0.05 5.0 100 0.2 batteries B
0.30 0.20 5.0 98 0.2 batteries C 0.40 0.20 7.0 98 0.2 batteries D
0.15 0.05 7.0 100 0.2 batteries E 0.20 0.10 6.0 100 0.2 batteries F
0.40 0.25 6.0 94 0.2 batteries G 0.15 0.10 4.5 100 0.6 batteries H
0.20 -- 4.5 98 0.6 batteries I 0.05 0.03 4.5 100 0.6 batteries J
0.01 0.01 2.0 100 1.0 batteries K 0.50 0.20 7.0 98 0.2 .sup.(note
1)indexes when the discharge time of batteries "A" at 500 mA (an
end-of-discharge voltage of 2.0 V) is 100 .sup.(note 2)values
measured at a sinusoidal alternating current of 1 kHz by supplying
a current of 0.1 mA
[0049] According to Table 1, the batteries "F" have a low initial
discharge performance. The reason for this is considered that the
high sodium content of the electrolytic manganese dioxide used as
the positive electrode active material causes the sodium contained
in positive electrode 1 to be deposited on negative electrode 2 and
to form a resistance film thereon, thereby impeding the discharge
reaction.
[0050] Table 1 also shows that the batteries "G", "H", "I", and "J"
have excellent initial discharge characteristics, but have high
internal resistances when continued to be discharged at 300
k.OMEGA. for one year, indicating that their long-term discharge
performance are poor. The reason for this is considered as follows.
Since the electrolytic manganese dioxides used as the positive
electrode active material have pHs of less than 5, the acid
generated from the reaction between sulfuric acid components
remaining in the electrolytic manganese dioxide and a small amount
of water in the batteries causes manganese ions to elute from
positive electrode 1, and to be deposited on negative electrode 2,
thus forming a resistance film.
[0051] In contrast, the batteries "A" to "E" and "K" have low
internal resistances when continued to be discharged at 300
k.OMEGA. for one year, indicating their excellent long-term
discharge performance as well as excellent initial discharge
performance. The batteries "K", however, require more water than
batteries "A" to "E" because the washing is performed using 40 kg
of water per 1 kg of the heat-treated electrolytic manganese
dioxide. In conclusion, in order to save water for the washing, the
sodium content of the neutralized electrolytic manganese dioxide is
preferably 0.1 to 0.4% by mass.
[0052] The above description shows cylindrical batteries having a
spiral-wound electrode assembly, but the present invention is not
limited to such an electrode assembly or battery shape. The present
invention is also applicable to batteries with stacked electrodes
or prismatic or coin shaped batteries.
INDUSTRIAL APPLICABILITY
[0053] The sodium-neutralized electrolytic manganese dioxide
according to the present invention can be a positive electrode
active material for lithium primary batteries excellent in both
initial discharge characteristics and long-term discharge
characteristics, thus being suitable for electrical devices which
are required to have a long life.
* * * * *